Conservation of Energy

Abstract

In his On the Conservation of Force, Helmholtz argued that by performing work on a body (or collection of bodies) one can either change its configuration or its speed. In the first case, the work is stored, so to speak, as potential energy. Examples of this are the lifting of a body to a new height or the stretching of a spring. The precise amount of work required—and the potential energy stored—depends on the force which must be overcome in order to change its configuration from an initial to a final state. In the second case, the work is stored as kinetic energy. The kinetic energy of a moving object is a measure of how much work the moving object can perform on another object (such as a target) before coming to a complete stop. Generally speaking, what we today call the energy of an object (or a configuration of objects) is just the amount of work which it is capable of performing. Moreover—and this is Helmholtz’s main point–this quantity of work seems to be conserved: when work is done on an object, the object can, in turn, do precisely the same amount of work on another object. This is what Helmholtz means when he states that “the quantity of force which can be brought into action in the whole of Nature is unchangeable, and can neither be increased nor diminished.” Thus far, Helmholtz has focused on mechanical systems, such as water-wheels, pendulums, windmills, pulleys and levers. Now, in the remainder of the essay, Helmholtz generalizes his previous analysis to consider steam engines, chemical affinity, batteries and electrical machines.